The general aim of the NACHO project was to determine how nicotinic signaling is participating in β-cell function in healthy and metabolically compromised conditions. We have performed a thorough analysis of nicotine’s effect on beta cell function in response to parasympathetic acetylcholine stimulation using cell lines, animal models and mouse and human tissue.
During these 2-year project we have done in vitro and in vivo experiments using mouse MIN6 beta cells and pancreatic islets from mice lacking nicotinic receptors and human donors. We performed pharmacological treatments with agonists of muscarinic (oxotremorine) or nicotinic (nicotine, varenicline (selective for β2/β4)) receptors or antagonists (mecamylamine) of nicotinic receptors and evaluated how they affected the acetylcholine-promoted glucose-stimulated insulin secretion (stimulation with glucose w/wo acetylcholine). We also evaluated whether these treatments affected mitochondrial activity (oxygen consumption rate, OCR) and calcium influx, being both critical molecular events during glucose-mediated insulin secretion.
In an in vivo study, we fed mice with a high fat diet and treated them with nicotine in drinking water for one month. After treatment, the lean and obese mice (w/wo nicotine) were subjected to 2DG-intraperitoneal glucose tolerance test (mimicking parasympathetic stimulation of insulin secretion) and analyzed the insulin secretion response in vivo. As expected, MafA mutant animals and islets (mouse model for beta cell dysfunction lacking nicotinic receptor expression) did not respond to acetylcholine and 2DG stimulation. Interestingly, we observed that long-term treatment of mice with nicotine reduced parasympathetic-promoted insulin secretion in lean but not obese mice. However, we observed no significant changes in the acetylcholine -promoted glucose-stimulated insulin secretion after short-term treatment with nicotine or nicotinic receptors agonist/inhibitors of MIN6 cells, mouse or human islets. Consistently, we did not observed changes in the acetylcholine-promoted glucose-stimulated mitochondrial oxygene consumption rate and cytosolic Ca2+ transients when MIN6 cells were treated with nicotinic receptors-directed drugs.
These results show that nicotine is affecting beta cell function after long-term in vivo treatment (similarily to smoking), most likely by impairing communication between nerve and beta cells. A hypothesis further supported by our related finding that blocking nicotinic signaling during beta cell development is impairing the formation of beta cell clusters and connection to nerve cells (see figure).
Dissemination of results: Two publications are planned during 2020 in open access journals.
